Mouse model of venous bypass graft arteriosclerosis

The ADP antagonist MRS2179 regulates the phenotype of smooth muscle cells to limit intimal hyperplasia

PURPOSE

ADP plays an important part in platelet aggregation by activating P2Y1 and P2Y12 receptors. The ADP antagonist MRS2179 has been used in thrombosis-related treatments but its effects on vein graft (VG) remodeling is undefined. We examined the effect of MRS2179 on VG intimal hyperplasia and explored the mechanism of action.

METHODS

A mouse model of VG transplantation was established. Mice underwent surgery and received MRS2179 by intraperitoneal injection every other day for 3 weeks. VG remodeling was assessed 4-weeks later. Vascular smooth muscle cells (VSMCs) were isolated and treated with MRS2179. The effect of MRS2179 on the proliferation, migration and inflammatory-cytokine expression of VSMCs was also evaluated.

RESULTS

MRS2179 significantly inhibited VSMC proliferation compared with the control group. Significant inhibitory effects of MRS2179 on VSMC migration was observed in two-dimensional and three-dimensional models. The extent of intimal hyperplasia was significantly less in MRS2179 treated mice than in controls. Reduced migration of macrophage was found in MRS2179 treated mice. Expression of the inflammatory cytokines IL-1β and TNF-α was decreased significantly in the MRS2179 treated group. In addition, decreased phosphorylation was found on Akt, Erk1/2 and p38.

CONCLUSIONS

These data demonstrate that MRS2179 inhibits neointima formation in VGs by regulating the proliferation, and migration of VSMCs, macrophage migration, inflammatory-cytokine secretion and related signaling pathway. Our study provides novel insights regarding purinergic signaling in SMCs in vivo. The P2Y1 receptor may serve as a therapeutic target in neointima formation.

Simultaneous Increases in Proliferation and Apoptosis of Vascular Smooth Muscle Cells Accelerate Diabetic Mouse Venous Atherosclerosis

Aims

This study was designed to demonstrate simultaneous increases in proliferation and apoptosis of vascular smooth muscle cells (VSMCs) leading to accelerated vein graft remodeling and to explore the underlying mechanisms.

Methods

Vein grafts were performed in non-diabetic and diabetic mice. The cultured quiescent VSMCs were subjected to mechanical stretch stress (SS) and/or advanced glycosylation end products (AGEs). Harvested vein grafts and treated VSMCs were used to detect cell proliferation, apoptosis, mitogen-activated protein kinases (MAPKs) activation and SM-α-actin expression.

Results

Significantly thicker vessel walls and greater increases in proliferation and apoptosis were observed in diabetic vein grafts than those in non-diabetic. Both SS and AGEs were found to induce different activation of three members of MAPKs and simultaneous increases in proliferation and apoptosis of VSMCs, and combined treatment with both had a synergistic effect. VSMCs with strong SM-α-actin expression represented more activated JNKs or p38MAPK, and cell apoptosis, while the cells with weak SM-α-actin expression demonstrated preferential activation of ERKs and cell proliferation. In contrast, inhibition of MAPKs signals triggered significant decreases in VSMC proliferation, and apoptosis. Treatment of the cells with RNA interference of receptor of AGEs (RAGE) also resulted in significant decreases in both proliferation and apoptosis.

Conclusions

Increased pressure-induced SS triggers simultaneous increases in proliferation and apoptosis of VSMCs in the vein grafts leading to vein arterializations, which can be synergistically accelerated by high glucose-induced AGEs resulting in vein graft atherosclerosis. Either SS or AGEs and their combination induce simultaneous increases in proliferation and apoptosis of VSMCs via different activation of three members of MAPKs resulting from different VSMC subtypes classified by SM-α-actin expression levels.

Heterotopic Cervical Heart Transplantation in Mice

The heterotopic cervical heart transplantation in mice is a valuable tool in transplant and cardiovascular research. The cuff technique greatly simplifies this model by avoiding challenging suture anastomoses of small vessels thereby reducing warm ischemia time. In comparison to abdominal graft implantation the cervical model is less invasive and the implanted graft is easily accessible for further follow-up examinations. Anastomoses are performed by pulling the ascending aorta of the graft over the cuff with the recipient's common carotid artery and by pulling the main pulmonary artery over the cuff with the external jugular vein. Selection of appropriate cuff size and complete mobilization of the vessels are important for successful revascularization. Ischemia-reperfusion (I/R) injury can be minimized by perfusing the graft with a cardioplegic solution and by hypothermia. In this article, we provide technical details for a simplified and improved cuff technique, which should allow surgeons with basic microsurgical skills to perform the procedure with a high success rate.

Perivascular mast cells regulate vein graft neointimal formation and remodeling

Objective. Emerging evidence suggests an important role for mast cells in vein graft failure. This study addressed the hypothesis that perivascular mast cells regulate in situ vascular inflammatory and proliferative responses and subsequent vein graft neointimal lesion formation, using an optimized local mast cell reconstitution method.

Methods and Results. Neointimal hyperplasia was induced by insertion of a vein graft into the right carotid artery in wild type and mast cell deficient Kit^{W−sh/W−sh} mice. In some experiments, mast cells were reconstituted systemically (tail vein injection of bone marrow-derived mast cells) or locally (directly into the right neck area) prior to vein grafting. Vein graft neointimal lesion formation was significantly (P < 0.05) reduced in Kit^{W−sh/W−sh} mice. Mast cell deficiency reduced the number of proliferating cells, and inhibited L-selectin, CCL2, M-CSF and MIP-3α expression in the vein grafts. Local but not systemic mast cell reconstitution restored a perivascular mast cell population that subsequently promoted neointimal formation in mast cell deficient mice.

Conclusion. Our data demonstrate that perivascular mast cells play a key role in promoting neointima formation by inducing local acute inflammatory and proliferative responses. These results suggest that ex vivo intraoperative targeting of mast cells may have therapeutic potential for the prevention of pathological vein graft remodeling.

Resveratrol-Induced Vascular Progenitor Differentiation towards Endothelial Lineage via MiR-21/Akt/β-Catenin Is Protective in Vessel Graft Models

Background and Purpose

Vessel graft failure is typically associated with arteriosclerosis, in which endothelial dysfunction/damage is a key event. Resveratrol has been shown to possess cardioprotective capacity and to reduce atherosclerosis. We aimed to study the influence of resveratrol on the behavior of resident stem cells that may contribute to graft arteriosclerosis.

Experimental Approach

Vascular resident progenitor cells and embryonic stem cells were treated with resveratrol under differentiating conditions and endothelial markers expression was evaluated. Expression of miR-21 and β-catenin was also tested and exogenously modified. Effects of resveratrol treatment in an ex vivo re-endothelialization model and on mice undergone vascular graft were evaluated.

Key Results

Resveratrol induced expression of endothelial markers such as CD31, VE-cadherin and eNOS in both progenitor and stem cells. We demonstrated that resveratrol significantly reduced miR-21 expression, which in turn reduced Akt phosphorylation. This signal cascade diminished the amount of nuclear β-catenin, inducing endothelial marker expression and increasing tube-like formation by progenitor cells. Both the inhibition of miR-21 and the knockdown of β-catenin were able to recapitulate the effect of resveratrol application. Ex vivo, progenitor cells treated with resveratrol produced better endothelialization of the decellularized vessel. Finally, in a mouse model of vessel graft, a resveratrol-enhanced diet was able to reduce lesion formation.

Conclusions and Implications

We provide the first evidence that oral administration of resveratrol can reduce neointimal formation in a model of vascular graft and elucidated the underpinning miR-21/Akt/β-catenin dependent mechanism. These findings may support the beneficial effect of resveratrol supplementation for graft failure prevention.

Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed.

Role of cAMP-phosphodiesterase 1C signaling in regulating growth factor receptor stability, vascular smooth muscle cell growth, migration, and neointimal hyperplasia

RATIONALE

Neointimal hyperplasia characterized by abnormal accumulation of vascular smooth muscle cells (SMCs) is a hallmark of occlusive disorders such as atherosclerosis, postangioplasty restenosis, vein graft stenosis, and allograft vasculopathy. Cyclic nucleotides are vital in SMC proliferation and migration, which are regulated by cyclic nucleotide phosphodiesterases (PDEs).

OBJECTIVE

Our goal is to understand the regulation and function of PDEs in SMC pathogenesis of vascular diseases.

METHODS AND RESULTS

We performed screening for genes differentially expressed in normal contractile versus proliferating synthetic SMCs. We observed that PDE1C expression was low in contractile SMCs but drastically elevated in synthetic SMCs in vitro and in various mouse vascular injury models in vivo. In addition, PDE1C was highly induced in neointimal SMCs of human coronary arteries. More importantly, injury-induced neointimal formation was significantly attenuated by PDE1C deficiency or PDE1 inhibition in vivo. PDE1 inhibition suppressed vascular remodeling of human saphenous vein explants ex vivo. In cultured SMCs, PDE1C deficiency or PDE1 inhibition attenuated SMC proliferation and migration. Mechanistic studies revealed that PDE1C plays a critical role in regulating the stability of growth factor receptors, such as PDGF receptor β (PDGFRβ) known to be important in pathological vascular remodeling. PDE1C interacts with low-density lipoprotein receptor-related protein-1 and PDGFRβ, thus regulating PDGFRβ endocytosis and lysosome-dependent degradation in an low-density lipoprotein receptor-related protein-1-dependent manner. A transmembrane adenylyl cyclase cAMP-dependent protein kinase cascade modulated by PDE1C is critical in regulating PDGFRβ degradation.

CONCLUSIONS

These findings demonstrated that PDE1C is an important regulator of SMC proliferation, migration, and neointimal hyperplasia, in part through modulating endosome/lysosome-dependent PDGFRβ protein degradation via low-density lipoprotein receptor-related protein-1.

C-reactive protein induces expression of tissue factor and plasminogen activator inhibitor-1 and promotes fibrin accumulation in vein grafts

BACKGROUND

C-reactive protein (CRP) promotes tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1) expression in vitro, and an elevated plasma CRP concentration is associated with an increased risk of vein graft (VG) thrombosis after coronary artery bypass surgery. However, little is known about the effects of CRP on VG TF and PAI-1 expression in vivo, or on VG thrombosis.

OBJECTIVES

We studied transgenic (Tg) mice expressing human CRP in a VG model to explore in vivo cause-and-effect relationships between CRP and TF, PAI-1, and VG thrombosis.

METHODS

Vein segments from wild-type (WT) and CRP-Tg donors were transplanted into carotid arteries of WT and CRP-Tg recipients. VGs were analyzed 1-4 weeks later.

RESULTS

Human CRP accumulated in VGs during the first 4 weeks after surgery, but appeared to originate exclusively from systemic sources, rather than local production. Human CRP significantly increased TF gene expression, protein concentration and activity in VGs. Human CRP also increased PAI-1 concentrations in VGs, although only in vascular endothelial cells. Human CRP stimulated macrophage migration, invasion into VGs, and TF expression. Fibrin deposition was significantly greater in VGs of CRP-Tg mice than in WT controls.

CONCLUSIONS

CRP accumulates in VGs early after surgery, originating from systemic sources rather than local synthesis. Human CRP promotes TF and PAI-1 expression in VGs, although with different expression patterns. Human CRP stimulates macrophage invasion and fibrin deposition within VGs. These results suggest that CRP induces pathologic changes in VGs that contribute to early VG occlusion.

Anti-inflammatory and anti-proliferative effects of CBS3830 in arterialized vein grafts in rats

OBJECTIVE

To investigated whether CBS3830, a highly selectively inhibitor of p38MAPK, could ameliorate inflammation and intimal hyperplasia in arterialized vein grafts (AVGs).

METHODS

Sixty male Sprague-Dawley rats underwent a reversed right jugular vein to common carotid artery interposition graft and were randomly treatment with vehicle (control) or single-dose (3 mg/kg, preoperative) or double-dose (3 mg/kg, preoperative and 4 d postoperative) CBS3830. Twenty rats underwent sham operation. The levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) were determined by ELISA. Vein grafts were analyzed by intimal/medial morphometry, proliferating cell nuclear antigen (PCNA) expression, and p38MAPK phosphorylation.

RESULTS

TNF-α, IL-1β, and IL-6 gradually increased then slowly decreased in AVG rats. However, at 4 d and 7 d, TNF-α levels decreased by 37.5% and 29.5% (p = 0.003, 0.05, respectively) in the single-dose CBS3830 group, and by 37.6% and 32.5%, respectively (both p = 0.003) in the double-dose group compared with those of control. IL-1β levels significantly reduced at 4 d and 14 d in both dosage groups. IL-6 levels significantly reduced at 7 d in both groups. Intima and medial thickening were significantly reduced in both dosage treated groups at 7, 14, and 28 d (all p = 0.000) compared to the controls. Further study showed CBS3830 inhibited p38MAPK phosphorylation and decreased PCNA expression.

CONCLUSIONS

CBS3830 significantly decreases inflammation and intimal hyperplasia in AVGs.

Smooth muscle cells from the anastomosed artery are the major precursors for neointima formation in both artery and vein grafts

Accumulation of smooth muscle cells (SMC) results in neointima formation in injured vessels. Two graft models consisting of vein and artery grafts were created by anastomosing common carotid arteries to donor vessels. To identify the origin of the neointima cells from anastomosed arteries, we use Wnt1-Cre/reporter mice to label and track SMCs in the common carotid artery. The contribution of SMCs in the neighboring arteries to neointima formation was studied. On evaluating the artery grafts after 1 month, >90 % of the labeled neointima cells were found to have originated from the anastomosing host arteries. Most of the neointima cells were also smooth muscle α-actin positive (SMA-α(+)) and expressed the smooth muscle myosin heavy chain (SMMHC), the SMC terminal differentiation marker. In vein grafts, about 60 % SMA-α-positive cells were from anastomosing arteries. Bone marrow cells did not contribute to neointima SMCs in vein grafts, but did co-stain with markers of inflammatory cells. Wnt1 expression was not detected in the neointima cells in the vein or artery grafts, or the injured femoral arteries. Neointima SMCs showed the synthetic phenotype and were positively labeled with BrdU in vitro and in vivo. Treatment with the IGF-1 receptor inhibitor suppressed SMC proliferation and neointima formation in vein grafts. Our results indicate that SMCs from the neighboring artery are predominantly present in the neointima formed in both vein and artery grafts and that Wnt1-Cre mice can be used to explore the role of SMCs originating from neighboring vessels in vascular remodeling.

Animal models of atherosclerosis and magnetic resonance imaging for monitoring plaque progression

Atherosclerosis, the main cause of heart attack and stroke, is the leading cause of death in most modern countries. Preventing clinical events depends on a better understanding of the mechanism of atherosclerotic plaque destabilization. Our knowledge on the characteristics of vulnerable plaques in humans has grown past decades. Histological studies have provided a precise definition of high-risk lesions and novel imaging methods for human atherosclerotic plaque characterization have made significant progress. However the pathological mechanisms leading from stable lesions to the formation of vulnerable plaques remain uncertain and the related clinical events are unpredictable. An animal model mimicking human plaque destablization is required as well as an in vivo imaging method to assess and monitor atherosclerosis progression. Magnetic resonance imaging (MRI) is increasingly used for in vivo assessment of atherosclerotic plaques in the human carotids. MRI provides well-characterized morphological and functional features of human atherosclerotic plaque which can be also assessed in animal models. This review summarizes the most common species used as animal models for experimental atherosclerosis, the techniques to induce atherosclerosis and to obtain vulnerable plaques, together with the role of MRI for monitoring atherosclerotic plaques in animals.

Contribution of endothelial injury and inflammation in early phase to vein graft failure: the causal factors impact on the development of intimal hyperplasia in murine models

OBJECTIVES

Autologous veins are preferred conduits in by-pass surgery. However, long-term results are hampered by limited patency due to intimal hyperplasia. Although mechanisms involved in development of intimal hyperplasia have been established, the role of inflammatory processes is still unclear. Here, we studied leukocyte recruitment and intimal hyperplasia in inferior vena cava grafts transferred to abdominal aorta in mice.

METHODS AND RESULTS

Several microscopic techniques were used to study endothelium denudation and regeneration and leukocyte recruitment on endothelium. Scanning electron microscopy demonstrated denudation of vein graft endothelium 7 days post-transfer and complete endothelial regeneration by 28 days. Examination of vein grafts transferred to mice transgenic for green fluorescent protein under Tie2 promoter in endothelial cells showed regeneration of graft endothelium from the adjacent aorta. Intravital microscopy revealed recruitment of leukocytes in vein grafts at 7 days in wild type mice, which had tapered off by 28 days. At 28 and 63 days there was significant development of intimal hyperplasia. In contrast; no injury, leukocyte recruitment nor intimal hyperplasia occurred in arterial grafts. Leukocyte recruitment was reduced in vein grafts in mice deficient in E- and P-selectin. In parallel, intimal hyperplasia was reduced in vein grafts in mice deficient in E- and P-selectin and in wild type mice receiving P-selectin/E-selectin function-blocking antibodies.

CONCLUSION

The results show that early phase endothelial injury and inflammation are crucial processes in intimal hyperplasia in murine vein grafts. The data implicate endothelial selectins as targets for intervention of vein graft disease.

Stem cells accumulate on a decellularized arterial xenograft in vivo

BACKGROUND

Surgical interest in complete arterial revascularization is expanding, but some patients lack suitable conduits for this goal. The field of stem cell biology is rapidly expanding and, together with the concepts of tissue engineering, offers the promise of growing autologous grafts in the laboratory. We aim to develop a model using human arteries as vascular grafts in a murine model and to assess the cellular accumulation on these grafts.

METHODS

Human arterial samples were collected and decellularized using an ionic detergent. These vessel scaffolds were then used as grafts in an in vivo mouse model, and the cellular accumulation on them was examined histologically and by cell culture with assessment of their physiologic properties.

RESULTS

Left internal mammary artery branches were fully decellularized and successfully implanted into a murine model. Grafts were repopulated by cells expressing stem cell markers cluster of differentiation 34 and stage-specific embryonic antigen, and subsequently expressed markers of mature endothelial and smooth muscle cells (cluster of differentiation 31, calponin, and myosin heavy chain). The migratory capacity of the cultured cells was significantly higher than that of mouse smooth muscle cells (p < 0.001).

CONCLUSIONS

We describe the successful use of human arteries in a murine graft model, allowing the study of repopulation. Decellularized grafts are repopulated by cells expressing stem cell markers and subsequently express smooth muscle and endothelial cell markers. This model has the potential to be used for further development of laboratory-grown vascular grafts.

Early growth response protein 1 promotes restenosis by upregulating intercellular adhesion molecule-1 in vein graft

OBJECTIVES

To verify the relationship between Egr-1 and vein graft restenosis and investigate the related mechanisms.

METHODS

Mouse vein graft models were established in Egr-1 knockout (KO) and wild-type (WT) mice. The vein grafts in the mice were taken for pathological examination and immunohistochemical analysis. The endothelial cells (ECs) were stimulated by using a computer-controlled cyclic stress unit. BrdU staining and PCR were used to detect ECs proliferation activity and Egr-1 and ICAM-1 mRNA expression, respectively. Western-blot analysis was also used to detect expression of Egr-1 and intercellular adhesion molecule-1 (ICAM-1) proteins.

RESULTS

The lumens of vein grafts in Egr-1 KO mice were wider than in WT mice. ECs proliferation after mechanical stretch stimulation was suppressed by Egr-1 knockout (P < 0.05). Both in vein grafts and ECs from WT mice after mechanical stretch stimulation, mRNA expression and protein of Egr-1 and ICAM-1 showed increases (P < 0.05). However, ICAM-1 expression was significantly suppressed in ECs from Egr-1 knockout mice (P < 0.05).

CONCLUSIONS

Egr-1 may promote ECs proliferation and result in vein graft restenosis by upregulating the expression of ICAM-1. As a key factor of vein graft restenosis, it could be a target for the prevention of restenosis after CABG surgery.

A new synthetic FGF receptor antagonist inhibits arteriosclerosis in a mouse vein graft model and atherosclerosis in apolipoprotein E-deficient mice

Objective

The role of fibroblast growth factors (FGFs) in the development of vascular diseases remains incompletely understood. The objective of this study was to examine the effects of a new small-molecule multi-FGF receptor blocker with allosteric properties, SSR128129E, on neointimal proliferation after a vein graft procedure in mice and on the development of atherosclerosis in atherosclerosis-prone apolipoprotein E (apoE)-deficient mice.

Methods and Results

Vein grafts were performed in 3 month-old male C57BL6 mice. Segments of the vena cava were interposed at the level of the carotid artery. In SSR128129E (50 mg/kg/d)-treated animals, a dramatic decrease in neointimal proliferation was observed 2 and 8 weeks after the graft (72.5 %, p<0.01, and 47.8 %, p<0.05, respectively). Four-week old male apoE-deficient mice were treated with SSR128129E (50 mg/kg/d) for 3 and 5 months in comparison with a control group. SSR128129E treatment resulted in a reduction of lesion size in the aortic sinus (16.4 % (ns) at 3 months and 42.9 % (p<0.01) at 5 months, without any change in serum lipids. SSR128129 significantly reduced FGFR2 mRNA levels in the aortic sinus (p<0.05, n=5-6), but did not affect the mRNA expression levels of other FGF receptors or ligands.

Conclusion

These studies indicate that FGFs have an important role in the development of vascular diseases like atherosclerosis and graft arteriosclerosis. These data suggest that inhibition of FGF receptors by compounds like SSR128129E might be useful as a new therapeutic approach for these vascular pathologies.

Tetrahydrobiopterin determines vascular remodeling through enhanced endothelial cell survival and regeneration

BACKGROUND

Endothelial cell (EC) survival and regeneration are important determinants of the response to vascular injury that leads to neointimal hyperplasia and accelerated atherosclerosis. Nitric oxide (NO) is a key regulator of EC and endothelial progenitor cell function, but the pathophysiological mechanisms that regulate endothelial NO synthase in endothelial regeneration remain unclear.

METHODS AND RESULTS

Endothelium-targeted overexpression of GTP cyclohydrolase (GCH) I increased levels of the endothelial NO synthase cofactor, tetrahydrobiopterin, in an EC-specific manner and reduced neointimal hyperplasia in experimental vein grafts in GCH/apolipoprotein E-knockout mice. These effects were mediated through enhanced donor-derived survival and recipient-derived repopulation of GCH transgenic ECs, revealed by tracking studies in Tie2-LacZ/GCH-Tg/apolipoprotein E-knockout recipient mice or donor grafts, respectively. Endothelial GCH overexpression increased endothelial NO synthase coupling and enhanced the proliferative capacity of ECs and circulating endothelial progenitor cell numbers after vascular injury.

CONCLUSIONS

These observations indicate that endothelial tetrahydrobiopterin availability modulates neointimal hyperplasia after vascular injury via accelerated EC repopulation and growth. Targeting tetrahydrobiopterin-dependent endothelial NO synthase regulation in the endothelium is a rational therapeutic target to enhance endothelial regeneration and reduce neointimal hyperplasia in vascular injury states.

Diet-induced obesity drives negative mouse vein graft wall remodeling

INTRODUCTION

The heightened inflammatory phenotype associated with obesity has been linked to the development of cardiovascular diseases. Short-term high-fat feeding induces a proinflammatory state that may impact the blood vessel wall. CD11c, a significantly increased dendritic cell biomarker during diet-induced obesity (DIO), may have a mechanistic role in this high-fat feeding effect. We hypothesized that the proinflammatory effect of short-term DIO accelerates vein bypass graft failure via CD11c-dependent mechanisms.

METHODS

Male 9-week-old DIO mice (n = 13, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) and normal chow controls (n = 15, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) underwent unilateral carotid interposition vein isografting (inferior vena cava from the same diet and genetic background donor), with a midgraft or outflow focal stenosis. Vein grafts were harvested at either 1 week (immunohistochemical staining for early CD11c expression) or 4 weeks later (morphometric analyses and CD11c evaluation).

RESULTS

Despite a 40% larger body size, C57BL/6J DIO mice had 44% smaller poststenosis vein graft lumens (P = .03) than their controls via an acceleration of overall negative vein graft wall remodeling in the day-28 midgraft focal stenosis model but not in the outflow stenosis model. Higher CD11c expression occurred in DIO midgraft-stenosis vein graft walls, both at postoperative days 7 and 28. In contrast, with in vivo CD11c deficiency, DIO did not elicit this poststenotic negative remodeling but attenuated intimal hyperplasia.

CONCLUSIONS

These findings highlight negative wall remodeling as a potential factor leading to vein graft failure and provide direct evidence that short-term dietary alterations in the mammalian metabolic milieu can have lasting implications related to acute vascular interventions. DIO induces negative mouse vein graft wall remodeling via CD11c-depedent pathways.

Pathology of Saphenous Vein Grafts

Saphenous vein grafts (SVGs) are the most used conduits in coronary artery bypass graft (CABG) surgery; however, they are susceptible to accelerated atherosclerosis. Clinical studies have shown 10-year patency rates of SVG can be as low as 50% to 60%. This article highlights changes that are observed following CABG surgery using SVG, including intimal thickening to the development of atherosclerotic changes, and how these changes in vein graft are different from those observed in native atherosclerosis. It also discusses the role of risk factors that contribute to acceleration of SVG atherosclerosis.

miRNA-21 is dysregulated in response to vein grafting in multiple models and genetic ablation in mice attenuates neointima formation

Aims

The long-term failure of autologous saphenous vein bypass grafts due to neointimal thickening is a major clinical burden. Identifying novel strategies to prevent neointimal thickening is important. Thus, this study aimed to identify microRNAs (miRNAs) that are dysregulated during neointimal formation and determine their pathophysiological relevance following miRNA manipulation.

Methods and results

We undertook a microarray approach to identify dysregulated miRNAs following engraftment in an interpositional porcine graft model. These profiling experiments identified a number of miRNAs which were dysregulated following engraftment. miR-21 levels were substantially elevated following engraftment and these results were confirmed by quantitative real-time PCR in mouse, pig, and human models of vein graft neointimal formation. Genetic ablation of miR-21 in mice or grafted veins dramatically reduced neointimal formation in a mouse model of vein grafting. Furthermore, pharmacological knockdown of miR-21 in human veins resulted in target gene de-repression and a significant reduction in neointimal formation.

Conclusion

This is the first report demonstrating that miR-21 plays a pathological role in vein graft failure. Furthermore, we also provided evidence that knockdown of miR-21 has therapeutic potential for the prevention of pathological vein graft remodelling.

Most important chronic complications of arteriovenous fistulas for hemodialysis

The aim of this review was to highlight the most important complications of arteriovenous fistulas (AVFs) for hemodialysis (HD). The quality of vascular access for HD should be suitable for repeated puncture and allow a high blood flow rate for high-efficiency dialysis with minimal complications. The dialysis staff must be well versed in manipulation of the AVF, and there should be a minimal need for corrective interventions. Construction of an AVF creates conditions for increasing the flow of blood through the venous system. Fulfillment of these conditions reduces the risk of turbulence and endothelium injury, which, in turn, minimizes the potential for stenosis. An AVF is closest to the ideal model of vascular access. The most important complications of fistulae for HD are lymphedema, infection, aneurysm, stenosis, congestive heart failure, steal syndrome, ischemic neuropathy and thrombosis. In HD patients, the most common cause of vascular access failure is neointimal hyperplasia. It is important to gain information about early clinical symptoms of AVF dysfunction in order to prevent and adequately treat potential complications.

Histological evaluation of age-related variations in saphenous vein grafts used for coronary artery bypass grafting

INTRODUCTION

Venous coronary artery bypass grafts (CABG) might undergo a process of arterialization resulting in neointimal formation and medial hypertrophy. It is often followed by critical occlusion of the graft lumen. The aim of the study was to assess histological representative features of saphenous vein reconstruction in aging as well as to establish optimal patients' age limits applicable for optimal selection of grafts.

MATERIAL AND METHODS

One hundred and ten patients undergoing venous CABG were divided into 4 age subgroups: (A) 50 years and less, (B) 51-60 years, (C) 61-70 years and (D) > 70 year-old subjects. Distal venous graft segments were saved for an adequate morphometric assay which was followed by suitable statistical analysis.

RESULTS

The entire venous wall thickness as well as its tunica media were found to become significantly thinner between subgroups A and D. The number of smooth muscle cell (SMC) nuclei within the tunica media did not differ between study subgroups. The majority of these nuclei in subgroup D were found, however, to be more elongated than in subgroup A (SMC length/width index in subgroup D was found to be significantly higher than in subgroup A).

CONCLUSIONS

Progressive, age-related thinning of the venous wall and tunica media as well as SMC nucleus elongation might suggest impairment of SMCs' migration and proliferation rate. Consequently, individuals aged 70 years and over may benefit clinically more from venous CABG than younger patients due to the lower risk of arterialization and occlusion of the graft lumen in the future.

Training a sophisticated microsurgical technique: interposition of external jugular vein graft in the common carotid artery in rats

Neointimal hyperplasia is one the primary causes of stenosis in arterialized veins that are of great importance in arterial coronary bypass surgery, in peripheral arterial bypass surgery as well as in arteriovenous fistulas.(1-5) The experimental procedure of vein graft interposition in the common carotid artery by using the cuff-technique has been applied in several research projects to examine the aetiology of neointimal hyperplasia and therapeutic options to address it. (6-8) The cuff prevents vessel anastomotic remodeling and induces turbulence within the graft and thereby the development of neointimal hyperplasia. Using the superior caval vein graft is an established small-animal model for venous arterialization experiment.(9-11) This current protocol refers to an established jugular vein graft interposition technique first described by Zou et al., (9) as well as others.(12-14) Nevertheless, these cited small animal protocols are complicated. To simplify the procedure and to minimize the number of experimental animals needed, a detailed operation protocol by video training is presented. This video should help the novice surgeon to learn both the cuff-technique and the vein graft interposition. Hereby, the right external jugular vein was grafted in cuff-technique in the common carotid artery of 21 female Sprague Dawley rats categorized in three equal groups that were sacrificed on day 21, 42 and 84, respectively. Notably, no donor animals were needed, because auto-transplantations were performed. The survival rate was 100 % at the time point of sacrifice. In addition, the graft patency rate was 60 % for the first 10 operated animals and 82 % for the remaining 11 animals. The blood flow at the time of sacrifice was 8±3 ml/min. In conclusion, this surgical protocol considerably simplifies, optimizes and standardizes this complicated procedure. It gives novice surgeons easy, step-by-step instruction, explaining possible pitfalls, thereby helping them to gain expertise fast and avoid useless sacrifice of experimental animals.

Plaque rupture complications in murine atherosclerotic vein grafts can be prevented by TIMP-1 overexpression

The current study describes the incidence and phenotype of plaque rupture complications in murine vein grafts. Since matrix metalloproteinases (MMPs) are highly involved in atherosclerotic plaque vulnerability and plaque rupture, we hypothesized that this model can be validated by overexpression of the MMP inhibitor TIMP-1. First we studied 47 vein grafts in hypercholesterolemic ApoE3*Leiden mice for the incidence of plaque complications. In 79% of these grafts, extensive lesions with plaque rupture complications like dissections, intraplaque hemorrhages or erosions with intramural thrombi were found. Next, in vivo Near-InfraRed-Fluorescence imaging demonstrated that electroporation mediated TIMP-1-overexpression reduced local MMP activity in vein grafts by 73% (p<0.01). This led to a 40% reduction in lesion-size after 28d (p = 0.01) and a more stable lesion phenotype with significant more smooth muscle cells (135%), collagen (47%) and significant less macrophages (44%) and fibrin (55%) than controls. More importantly, lesions in the TIMP-1 group showed a 90% reduction of plaque complications (10/18 of control mice showed plaque complications versus 1/18 in TIMP-1 treated mice). Murine vein grafts are a relevant spontaneous model to study plaque stability and subsequent hemorrhagic complications, resulting in plaque instability. Moreover, inhibition of MMPs by TIMP-1-overexpression resulted in decreased plaque progression, increased stabilization and decreased plaque rupture complications in murine vein grafts.

Pathology of drug-eluting versus bare-metal stents in saphenous vein bypass graft lesions

OBJECTIVES

The purpose of this study was to assess the pathological responses of atherosclerotic saphenous vein bypass grafts (SVBGs) to drug-eluting stents (DES) versus bare-metal stents (BMS).

BACKGROUND

Repeat bypass surgery is typically associated with a high rate of morbidity and mortality. Percutaneous coronary interventions have emerged as the preferred treatment; however, only limited data are available on SVBGs pathological responses to DES and BMS.

METHODS

Formalin-fixed SVBG of >2 years duration (n = 31) were collected to histologically characterize advanced atherosclerotic lesions in native SVBG. In a separate group, SVBGs treated with DES (n = 9) and BMS (n = 9) for >30 days duration were assessed for morphological and morphometric changes.

RESULTS

Necrotic core lesions were identified in 25% of SVBG sections, and plaque rupture with luminal thrombosis was observed in 6.3% of histological sections (32% [10 of 31] vein grafts examined). Morphometry of DES demonstrated reduction in neointimal thickening versus BMS (0.13 mm [interquartile range: 0.06 to 0.16 mm] vs. 0.30 mm [interquartile range: 0.20 to 0.48 mm], p = 0.004). DES lesions also showed greater delayed healing characterized by increased peristrut fibrin deposition, higher percentage of uncovered struts, and less endothelialization compared with BMS. Stent fractures (DES 56% vs. BMS 11%, p = 0.045) and late stent thrombosis (DES 44% vs. BMS 0%, p = 0.023) were more common in DES versus BMS.

CONCLUSIONS

Advanced SVBG atherosclerotic lesions are characterized by large hemorrhagic necrotic cores. Stenting of such lesions is associated with delayed vascular healing and late thrombosis particularly following DES implantation, which may help explain the higher rates of cardiovascular events observed in SVBG stenting as compared with native coronary arteries.

Contribution of stem cells to neointimal formation of decellularized vessel grafts in a novel mouse model

Artificial vessel grafts are often used for the treatment of occluded blood vessels, but neointimal lesions commonly occur. To both elucidate and quantify which cell types contribute to the developing neointima, we established a novel mouse model of restenosis by grafting a decellularized vessel to the carotid artery. Typically, the graft developed neointimal lesions after 2 weeks, resulting in lumen closure within 4 weeks. Immunohistochemical staining revealed the presence of endothelial and smooth muscle cells, monocytes, and stem/progenitor cells at 2 weeks after implantation. Explanted cultures of neointimal tissues displayed heterogeneous outgrowth in stem cell medium. These lesional cells expressed a panel of stem/progenitor markers, including c-kit, stem cell antigen-1 (Sca-1), and CD34. Furthermore, these cells showed clonogenic and multilineage differentiation capacities. Isolated Sca-1(+) cells were able to differentiate into endothelial and smooth muscle cells in response to vascular endothelial growth factor (VEGF) or platelet-derived growth factor (PDGF)-BB stimulation in vitro. In vivo, local application of VEGF to the adventitial side of the decellularized vessel increased re-endothelialization and reduced neointimal formation in samples at 4 weeks after implantation. A population of stem/progenitor cells exists within developing neointima, which displays the ability to differentiate into both endothelial and smooth muscle cells and can contribute to restenosis. Our findings also indicate that drugs or cytokines that direct cell differentiation toward an endothelial lineage may be effective tools in the prevention or delay of restenosis.

RAGE mediates accelerated diabetic vein graft atherosclerosis induced by combined mechanical stress and AGEs via synergistic ERK activation

Aims/Hypothesis

Diabetes with hypertension rapidly accelerates vascular disease, but the underlying mechanism remains unclear. We evaluated the hypothesis that the receptor of advanced glycation end products (RAGE) might mediate combined signals initiated by diabetes-related AGEs and hypertension-induced mechanical stress as a common molecular sensor.

Methods

In vivo surgical vein grafts created by grafting vena cava segments from C57BL/6J mice into the common carotid arteries of streptozotocin (STZ)-treated and untreated isogenic mice for 4 and 8 weeks were analyzed using morphometric and immunohistochemical techniques. In vitro quiescent mouse vascular smooth muscle cells (VSMCs) with either knockdown or overexpression of RAGE were subjected to cyclic stretching with or without AGEs. Extracellular signal-regulated kinase (ERK) phosphorylation and Ki-67 expression were investigated.

Results

Significant increases in neointimal formation, AGE deposition, Ki-67 expression, and RAGE were observed in the vein grafts of STZ-induced diabetic mice. The highest levels of ERK phosphorylation and Ki-67 expression in VSMCs were induced by simultaneous stretch stress and AGE exposure. The synergistic activation of ERKs and Ki-67 in VSMCs was significantly inhibited by siRNA-RAGE treatment and enhanced by over-expression of RAGE.

Conclusion

RAGE may mediate synergistically increased ERK activation and VSMC proliferation induced by mechanical stretching with and without AGEs. It may serve as a common molecular bridge between the two, accelerating vascular remodeling. This study provides potential drug targets and novel therapeutic strategies for the treatment of vascular diseases resulting from diabetes with hypertension.

Oversized vein grafts develop advanced atherosclerosis in hypercholesterolemic minipigs

Background

Accelerated atherosclerosis is the main cause of late aortocoronary vein graft failure. We aimed to develop a large animal model for the study of pathogenesis and treatment of vein graft atherosclerosis.

Methods

An autologous reversed jugular vein graft was inserted end-to-end into the transected common carotid artery of ten hypercholesteroemic minipigs. The vein grafts were investigated 12-14 weeks later with ultrasound and angiograpy in vivo and microscopy post mortem.

Results

One minipig died during follow up (patent vein graft at autopsy), and one vein graft thrombosed early. In the remaining eight patent vein grafts, the mean (standard deviation) intima-media thickness was 712 μm (276 μm) versus 204 μm (74 μm) in the contralateral control internal jugular veins (P < .01). Advanced atherosclerotic plaques were found in three of four oversized vein grafts (diameter of graft > diameter of artery). No plaques were found in four non-oversized vein grafts (P < .05).

Conclusions

Our model of jugular vein graft in the common carotid artery of hypercholesterolemic minipigs displayed the components of human vein graft disease, i.e. thrombosis, intimal hyperplasia, and atherosclerosis. Advanced atherosclerosis, the main cause of late failure of human aortocoronary vein grafts was only seen in oversized grafts. This finding suggests that oversized vein grafts may have detrimental effects on patient outcome.

Mouse vein graft hemodynamic manipulations to enhance experimental utility

Mouse models serve as a tool to study vein graft failure. However, in wild-type mice, there is limited intimal hyperplasia, hampering efforts to identify anti-intimal hyperplasia therapies. Furthermore, vein graft wall remodeling has not been well quantified in mice. We hypothesized that simple hemodynamic manipulations can reproducibly augment intimal hyperplasia and remodeling end points in mouse vein grafts, thereby enhancing their experimental utility. Mouse inferior vena cava-to-carotid interposition isografts were completed using an anastomotic cuff technique. Three flow restriction manipulations were executed by ligating outflow carotid branches, creating an outflow common carotid stenosis, and constructing a midgraft stenosis. Flowmetry and ultrasonography were used perioperatively and at day 28. All ligation strategies decreased the graft flow rate and wall shear stress. Morphometry showed that intimal thickness increased by 26% via carotid branch ligation and by 80% via common carotid stenosis. Despite similar mean flow rates and shear stresses among the three manipulations, the flow waveform amplitudes were lowest with common carotid stenosis. The disordered flow of the midgraft stenosis yielded poststenotic dilatation. The creation of an outflow common carotid stenosis generates clinically relevant (poor runoff) vein graft low wall shear stress and offers a technically flexible method for enhancing the intimal hyperplasia response. Midgraft stenosis exhibits poststenotic positive wall remodeling. These reproducible approaches offer novel strategies for increasing the utility of mouse vein graft models.

Animal, in vitro, and ex vivo models of flow-dependent atherosclerosis: role of oxidative stress

Atherosclerosis is an inflammatory disease preferentially occurring in curved or branched arterial regions, whereas straight parts of the arteries are protected, suggesting a close relationship between flow and atherosclerosis. However, evidence directly linking disturbed flow to atherogenesis is just emerging, thanks to the recent development of suitable animal models. In this article, we review the status of various animal, in vitro, and ex vivo models that have been used to study flow-dependent vascular biology and atherosclerosis. For animal models, naturally flow-disturbed regions such as branched or curved arterial regions as well as surgically created models, including arterio-venous fistulas, vascular grafts, perivascular cuffs, and complete, incomplete, or partial ligation of arteries, are used. Although in vivo models provide the environment needed to mimic the complex pathophysiological processes, in vitro models provide simple conditions that allow the study of isolated factors. Typical in vitro models use cultured endothelial cells exposed to various flow conditions, using devices such as cone-and-plate and parallel-plate chambers. Ex vivo models using isolated vessels have been used to bridge the gap between complex in vivo models and simple in vitro systems. Here, we review these flow models in the context of the role of oxidative stress in flow-dependent inflammation, a critical proatherogenic step, and atherosclerosis.

Multifaceted role of plasminogen activator inhibitor-1 in regulating early remodeling of vein bypass grafts

OBJECTIVE

The role of plasminogen activator inhibitor-1 (PAI-1) in vein graft (VG) remodeling is undefined. We examined the effect of PAI-1 on VG intimal hyperplasia and tested the hypothesis that PAI-1 regulates VG thrombin activity.

METHODS AND RESULTS

VGs from wild-type (WT), Pai1(-/-), and PAI-1-transgenic mice were implanted into WT, Pai1(-/-), or PAI-1-transgenic arteries. VG remodeling was assessed 4 weeks later. Intimal hyperplasia was significantly greater in PAI-1-deficient mice than in WT mice. The proliferative effect of PAI-1 deficiency was retained in vitronectin-deficient mice, suggesting that PAI-1's antiproteolytic function plays a key role in regulating intimal hyperplasia. Thrombin-induced proliferation of PAI-1-deficient venous smooth muscle cells (SMC) was significantly greater than that of WT SMC, and thrombin activity was significantly higher in PAI-1-deficient VGs than in WT VGs. Increased PAI-1 expression, which has been associated with obstructive VG disease, did not increase intimal hyperplasia.

CONCLUSIONS

Decreased PAI-1 expression (1) promotes intimal hyperplasia by pathways that do not require vitronectin and (2) increases thrombin activity in VG. PAI-1 overexpression, although it promotes SMC migration in vitro, did not increase intimal hyperplasia. These results challenge the concept that PAI-1 drives nonthrombotic obstructive disease in VG and suggest that PAI-1's antiproteolytic function, including its antithrombin activity, inhibits intimal hyperplasia.

Simvastatin exerts favourable effects on neointimal formation in a mouse model of vein graft

BACKGROUND

Simvastatin inhibits human saphenous vein neointima formation in human saphenous vein organ cultures. However, it is not known if simvastatin actually inhibits vein graft intima hyperplasia in vivo, and the underlying mechanisms behind that. In this study, we used a murine vein graft model to address these issues.

METHODS AND RESULTS

Vein grafting was performed among C57BL/6 J mice treated with low-dose (2 mg kg(-1)) or high-dose (20 mg kg(-1)) simvastatin or vehicle subcutaneously 72 h before and then daily after surgery. As compared to the vehicle, simvastatin dose-dependently significantly inhibited vein graft intima hyperplasia 4 weeks after surgeries. Immunohistochemistry studies suggested that vein graft neointima was mainly composed of vascular smooth muscle cells (VSMCs), and the rate of proliferating cell nuclear antigen (PCNA)-positive cells in the intima of vein grafts was significantly lower in simvastatin-treated groups than in control group. We isolated VSMC from mouse vena cava, simvastatin significantly reduced VSMC proliferation, and platelet-derived growth factor (PDGF)-induced VSMC migration in a dose-dependent manner.

CONCLUSION

Simvastatin inhibits neointima formation of mouse vein graft under normocholesterolaemic condition in vivo, the mechanisms might be associated with inhibitory effects of simvastatin on VSMC proliferation and migration.

Rapamycin-loaded nanoparticles for inhibition of neointimal hyperplasia in experimental vein grafts

Background

Nanoparticles possess several advantages as a carrier system for intracellular delivery of therapeutic agents. Rapamycin is an immunosuppressive agent which also exhibits marked antiproliferative properties. We investigated whether rapamycin-loaded nanoparticles(NPs) can reduce neointima formation in a rat model of vein graft disease.

Methods

Poly(lactic-co-glycolic acid) (PLGA) NPs containing rapamycin was prepared using an oil/water solvent evaporation technique. Nanoparticle size and morphology were determined by dynamic light scattering methodology and electron microscopy. In vitro cytotoxicity of blank, rapamycin-loaded PLGA (RPLGA) NPs was studied using MTT Assay. Excised rat jugular vein was treated ex vivo with blank-NPs, or rapamycin-loaded NPs, then interposed back into the carotid artery position using a cuff technique. Grafts were harvested at 21 days and underwent morphometric analysis as well as immunohistochemical analysis.

Results

Rapamycin was efficiently loaded in PLGA nanoparticles with an encapsulation efficiency was 87.6%. The average diameter of NPs was 180.3 nm. The NPs-containing rapamycin at 1 ng/ml significantly inhibited vascular smooth muscular cells proliferation. Measurement of rapamycin levels in vein grafts shown that the concentration of rapamycin in vein grafts at 3 weeks after grafting were 0.9 ± 0.1 μg/g. In grafted veins without treatment intima-media thickness was 300.4 ±181.5 μm after grafting 21 days. Whereas, Veins treated with rapamycin-loaded NPs showed a reduction of intimal-media thickness of 150.2 ± 62.5 μm (p = 0.001). CD-31 staining was used to measure luminal endothelial coverage in grafts and indicated a high level of endothelialization in 21 days vein grafts with no significant effect of blank or rapamycin-loaded NPs group.

Conclusions

We conclude that sustained-release rapamycin from rapymycin loaded NPs inhibits vein graft thickening without affecting the reendothelialization in rat carotid vein-to-artery interposition grafts and this may be a promising therapy for the treatment of vein graft disease.

Heat shock protein 60 and immune inflammatory responses in atherosclerosis

Hallmarks of inflammation in various cardiovascular diseases, notably atherosclerosis, have been observed for a long time. However, evidence for an (auto)antigen-driven process at these sites of inflammation has come forward only recently. Heat shock proteins (HSPs) have been identified as playing either immunologically mediated disease promoting or protective roles. HSP60 has been shown to trigger innate and adaptive immune responses that initiate the earliest still reversible inflammatory stage of atherosclerosis. HSP60 is structurally highly conserved and abundantly expressed by prokaryotic and eukaryotic cells under stressful conditions. Beneficial protective immunity to microbial HSP60 acquired by infection or vaccination and bona fide autoimmunity to biochemically altered autologous HSP60 is present in all humans. In vitro and in vivo experiments have demonstrated that classical atherosclerosis risk factors can act as endothelial stressors that provoke the simultaneous expression of adhesion molecules and of HSP60 in mitochondria, in cytoplasm, and on the cell surface, where it acts as a "danger signal" for cellular and humoral immune reactions. Hence, protective, preexisting anti-HSP60 immunity may have to be "paid for" by harmful (auto)immune cross-reactive attack on arterial endothelial cells maltreated by atherosclerosis risk factors. These experimentally and clinically proven findings are the basis for the autoimmune concept of atherosclerosis.

Smooth muscle cells in porcine vein graft intimal hyperplasia are derived from the local vessel wall

BACKGROUND

Accelerated intimal hyperplasia (IH) is an important cause of morbidity and mortality in patients with atherosclerotic vascular disease treated with bypass vein grafts. We used an interposition vein graft model to determine the source of neointimal cells in a clinically relevant large animal model.

METHODS

Jugular vein segments from sex-mismatched, MHC-in-bred pigs were implanted into common carotid arteries bilaterally and harvested up to 8 weeks postsurgery for stereological, histological, and immunofluorescence analyses.

RESULTS

Progressive IH lesions contained macrophages and smooth muscle cells (SMC). Fluorescent in situ hybridization following grafting of female veins into male arteries revealed that only ∼10% of the SMC were male, confirming that the majority of intimal SMC derived from the local vessel wall.

CONCLUSIONS

The majority of neointimal SMC in the IH seen after interposition vein grafting derive from the engrafted local vessel wall. These are the first results from a clinically relevant large animal model that confirm data from rodent models. They have implications for the utility of therapeutic stem cells in this type of intimal hyperplasia.

Rationale and practical techniques for mouse models of early vein graft adaptations

Mouse models serve as relatively new yet powerful research tools to study intimal hyperplasia and wall remodeling of vein bypass graft failure. Several model variations have been reported in the past decade. However, the approach demands thoughtful preparation, selected sophisticated equipment, microsurgical technical expertise, advanced tissue processing, and data acquisition. This review compares several described models and aims (building on our personal experiences) to practically aid the investigators who want to utilize mouse models of vein graft failure.

A novel urokinase receptor-targeted inhibitor for plasmin and matrix metalloproteinases suppresses vein graft disease

AIMS

Matrix metalloproteinases (MMP) and plasminogen activator (PA)/plasmin-mediated proteolysis, especially at the cell surface, play important roles in matrix degeneration and smooth muscle cell migration, which largely contributes to vein graft failure. In this study, a novel hybrid protein was designed to inhibit both protease systems simultaneously. MMP and plasmin activity were inhibited at the cell surface by this hybrid protein, consisting of the receptor-binding amino-terminal fragment (ATF) of urokinase-type PA, linked to both the tissue inhibitor of metalloproteinases (TIMP-1) and bovine pancreas trypsin inhibitor (BPTI), a potent protease inhibitor. The effect of overexpression of this protein on vein graft disease was studied.

METHODS AND RESULTS

A non-viral expression vector encoding the hybrid protein TIMP-1.ATF.BPTI was constructed and validated. Next, cultured segments of human veins were transfected with this vector. Expressing TIMP-1.ATF.BPTI in vein segments resulted in a mean 36 ± 14% reduction in neointima formation after 4 weeks. In vivo inhibition of vein graft disease by TIMP-1.ATF.BPTI is demonstrated in venous interpositions placed into carotid arteries of hypercholesterolaemic APOE*3Leiden mice. After 4 weeks, vein graft thickening was significantly inhibited in mice treated with the domains TIMP-1, ATF, or BPTI (36-49% reduction). In the TIMP-1.ATF.BPTI-treated mice, vein graft thickening was reduced by 67±4%, which was also significantly stronger when compared with the individual components.

CONCLUSION

These data provide evidence that cell surface-bound inhibition of the PA and MMP system by the hybrid protein TIMP-1.ATF.BPTI, overexpressed in distant tissues after electroporation-mediated non-viral gene transfer, is a powerful approach to prevent vein graft disease.

Inflammatory cell recruitment in cardiovascular disease: murine models and potential clinical applications

Atherosclerosis is the pathological process that underlies the development of cardiovascular disease, a leading cause of mortality. Atherosclerotic plaque formation is driven by the recruitment of inflammatory monocytes into the artery wall, their differentiation into macrophages and the subsequent transformation of macrophages into cholesterol-laden foam cells. Models of hypercholesterolaemia such as the ApoE (apolipoprotein E)-/- mouse and the application of transgenic technologies have allowed us to undertake a thorough dissection of the cellular and molecular biology of the atherosclerotic disease process. Murine models have emphasized the central role of inflammation in atherogenesis and have been instrumental in the identification of adhesion molecules that support monocyte recruitment, scavenger receptors that facilitate cholesterol uptake by macrophages and other macrophage activation receptors. The study of mice deficient in multiple members of the chemokine family, and their receptors, has shown that chemokines play a critical role in promoting atherosclerotic plaque formation. In the present review, we will discuss novel therapeutic avenues for the treatment of cardiovascular disease that derive directly from our current understanding of atherogenesis gained in experimental animal models.